 웃음 లి విె, గ్తిలులుread పాడ unters share ?? So, we are starting this video. Pause the video for a while and recall what is PTM. So, PTM is pulse time modulation. It is the class of signaling technique that encodes the sample values of analog signal onto time axis of digital signal. So, PTM is divided into two types. One is a pulse width modulation. And another is a pulse position modulation. In this session, we are going to study the demodulation of this PTM. Before that, we will see what is demodulation. Demodulation, it is the process of extracting original information from modulated signal. So, input to the demodulator, it is modulated signal and output is of original information or modulating signal. So, first let us see PWM demodulation. In the PWM demodulation technique, the PWM signal is given input to the demodulator and its output is the original information signal or modulating signal. So, in the PWM signal, the width is variable and amplitude and position of this pulses constant. So, the information contained in terms of change in width of this signal. Let us see the demodulator circuit. In the demodulator circuit, there are two parts. First part, it is the transistors circuit and the second part, it is nothing but this low pass filter circuit where the op-amp circuit is used. So, we will see this first transistors circuit. In this circuit, there are two transistors are used, transistor T1 and transistor T2. The input to this transistor T1, this is the PWM signal pulse width modulated signal. Now, the output of this signal, we will see at the collector of this transistor T2. As the information in PWM signal is in the form of change in width of this signal. So, we will see the working of this circuit when the input is given during the time interval a to b. So, during this time interval a to b, the input to this transistor T1, this input is a high signal. Then at that time, this transistor here basically works as an inverter. So, when we give the high input pulse to the transistor T1, then its output is a low pulse for that same duration. And this low pulse signal is given to the base of transistor T2. Then at that time, this T2 works in a cut-off region. So, it acts as an open switch. So, the movement at which the T2 works in a cut-off region, this capacitor starts charging through this RC circuit. And this capacitor charges up to the end of the pulse. Means this capacitor charges up to point b. So, for a time duration a to b, the charging voltages of this capacitor appears at this collector. So, this charging voltage is proportional to the width of this pulse. Now next, when we give the low pulse, means during the time interval b to c, when we give low pulse, input pulse to this base of the transistor T1, then its output of this transistor T1 gives the high pulse. So, this high pulse is applied to the base of the transistor T2. So, at this time, this T2 works in a saturation region. So, the capacitor which is present here, this capacitor rapidly discharged. And this is at the point b. So, in this way, this charging and discharging of this capacitor, this voltage appears at the collector of transistor T2. So, if you see the wave at the collector of transistor T2, that waves are nothing but similar to the sawtooth wave. And its envelope is proportional to the modulating signal. So, here the information is present in this envelope of this waveform. Now, when this signal or when this sawtooth wave is given input to the second-order op-amp low-pass filter, then with the help of this RC circuit, this op-amp circuit filters this input signal, means it pass the all-low frequency and it removes the higher frequency. So, at the output of this low-pass filter, we get a modulating signal. So, in this way, the PWM signal is demodulated at the output of this low-pass filter. Now, next is a PPM demodulation. In the PPM demodulation, the pulse position modulated signal is given input to the demodulator. And at the output of demodulator, we get a original information or continuous time signal. So, in the PPM signal, the width and amplitude of all pulses same, but there is a change in the position of this signal. Now, this is the PPM demodulator circuit. In this PPM demodulator circuit, again there are two parts. First is this transducerized circuit and second part is low-pass filter. Let us see the working of this transducerized circuit. Here, the input to this transistor, this is PPM signal. As we know that the information in PPM signal is in the form of change in position of this pulses, means the information present in the gap in between the pulses. So, during the time interval A to B, when the low signal is given to the base of this transistor, then at that time this transistor works in a cut-off region. So, it acts as an open switch. So, for this time period, this capacitor starts charging. This capacitor charges up to point B. So, the charging voltage of this capacitor, this charging voltage is proportional to the gap between these two pulses. So, the capacitor will charge from A to B. Now next, during the time interval B to C, here the high input pulse. So, when we apply this high input pulse to the base of this transistor T1, then at that time this transistor works in a saturation region. When we apply the high input pulse to the base of this transistor, this transistor works in a saturation region and it acts as a closed switch. So, at that time this capacitor discharge rapidly. So, this discharging voltage appears across this collector. In this way, if we see the waveform at the collector of this transistor, then we get a short-thwave and whose envelope is proportional to the modulating signal or original signal. So, here the information contains in the envelope of this signal. Now, when we apply this input short-thwave to this low-pass filter, at that time this open circuit removes the higher frequency and it passes all the lower frequency and we get the desired signal, demodulated signal at the output of this circuit. So, in this way the PPM signal is demodulated into the original signal or original information. These are the references. Thank you.